The NASA/ESA Hubble Space Telescope has snapped a view of several star generations in the central region of the Whirlpool Galaxy (M51), a spiral region 23 million light-years from Earth in the constellation Canes Venatici (the Hunting Dogs).
The galaxy's massive center, the bright ball of light in the center of the photograph, is about 80 light-years across and has a brightness of about 100 million suns. Astronomers estimate that it is about 400 million years old and has a mass 40 million times larger than our Sun. The concentration of stars is about 5,000 times higher than in our solar neighborhood, the Milky Way Galaxy. We would see a continuously bright sky if we lived near the bright center.
The dark "y" across the center is a sign of dust absorption. The bright dot in the middle of the "y" has a brightness of about one million suns, but a size of less than five light-years. Its power and its tiny size suggest that we have located the elusive central black hole that produces powerful radio jets.
Surrounding the center is a much older stellar population that covers a region of about 1,500 light-years in diameter and is at least 8 billion years old, and may be as old as the Universe itself, about 13 billion years.
Further away, there is a "necklace" of very young star-forming regions, clusters of infant stars, younger than 10 million years, which are about 700 light-years away from the center. Normally, young stars are found thousands of light-years away.
Astronomers believe that stars in the central region were formed when a dwarf companion galaxy - which is not in the photograph - passed close to it, about 400 million years ago, stirring up dust and material for new star birth. The close encounter has been felt for a long time and is believed to be responsible also for the unusually high star formation activity in the bright necklace of young stars.
The color image was assembled from four exposures taken Jan. 15, 1995 with Wide Field Planetary Camera-2 in blue, green, and red wavelengths.